1. Field of the Invention
The present invention relates to valve timing control for an internal combustion engine, which is made to learn a maximum retardation position in the valve timing.
2. Description of the Related Art
Conventionally, an apparatus is known which variably controls the valve timing of at least the intake valves or the exhaust valves according to engine operating conditions.
In addition, a system for controlling such an apparatus is well known, as disclosed in Japanese Patent Application Laid-open No. 9-345264. Referring to FIGS. 11 to 19, a description will be made hereinbelow of a conventional valve timing control system for an internal combustion engine.
FIG. 11 schematically shows the configuration of an internal combustion gasoline engine system having a common variable valve timing actuator.
In FIG. 11, an internal combustion engine 1 is composed of a plurality of (for example, four) cylinders which constitute a main body thereof. In this illustration, only one cylinder of the internal combustion engine 1 is shown.
A cylinder block 2 forms a cylinder portion of the internal combustion engine 1. A cylinder head 3 is connected to a top portion of the cylinder block 2.
A piston 4 is accommodated in each of the cylinders in the cylinder block 2, and is made to reciprocate up and down. A crank shaft 5, being connected to a lower end portion of the piston 4, is driven to rotate in accordance with the vertical movements of the piston 4.
A crank angle sensor 6 is made up of an electromagnetic pickup installed in the vicinity of the crank shaft 5, and outputs a crank angle signal SGT in synchronism with the rotation of the crank shaft 5 of the internal combustion engine 1. The crank angle signal SGT is used for detecting the speed Ne of the internal combustion engine 1 and further for detecting if the crank shaft 5 is at a predetermined reference crank angle (degCA).
A signal rotor 7 is connected integrally with the crank shaft 5, and has, at its outer circumference, two teeth 7a made of a magnetic substance and arranged at an interval of 180.degree. rotation angle. The crank angle sensor 6 generates a pulse-like crank angle signal SGT whenever either of the teeth 7a passes in front of the crank angle sensor 6.
A combustion chamber 8 is defined by an inner wall of the cylinder block 2, an inner wall of the cylinder head 3 and the top of the piston 4, and an air-fuel mixture introduced into the internal combustion engine 1 is combusted therein. An ignition plug 9 is installed in the top portion of the cylinder head 3 such that it protrudes into the interior of the combustion chamber 8, and ignites the air-fuel mixture by discharging.
A distributor 10 is connected to an exhaust side cam shaft 20 (which will be described herein later) in the cylinder head 3, and successively applies a high voltage for ignition to the ignition plug 9 of each of the cylinders. An igniter 11 generates the high ignition voltage.
Each of the ignition plugs 9 is coupled through a high-tension cord (not shown) to the distributor 10, and the high voltage output from the igniter 11 is distributed through the distributor 10 to each of the ignition plugs 9 in synchronism with the rotation of the crank shaft 5.
A water temperature sensor 12 is located in the cylinder block 2 to sense the temperature W of a coolant (coolant temperature) flowing in a coolant passage. An intake port 13 is provided on the intake side of the cylinder head 3, while an exhaust port 14 is provided on the exhaust side of the cylinder head 3.
An intake passage 15 communicates with the intake port 13, while an exhaust passage 16 communicates with the exhaust port 14. An intake valve 17 is placed in the intake port 13 of the cylinder head 3, while an exhaust valve 18 is placed in the exhaust port 14 of the cylinder head 3.
An intake side cam shaft 19 is situated above the intake valve 17 to open and close the intake valve 17, while an exhaust side cam shaft 20 is situated above the exhaust valve 18 to open and close the exhaust valve 18.
An intake side timing pulley 21 is mounted on one end portion of the intake side cam shaft 19, while an exhaust side timing pulley 22 is mounted on one end portion of the exhaust side cam shaft 20. A timing belt 23 makes a connection of the timing pulleys 21, 22 to the crank shaft 5. Each of the cam shafts 19, 20 is made to rotate at a speed being 1/2 of that of the crank shaft 5.
In an operation of the internal combustion engine 1, the rotational drive force of the crank shaft 5 is transmitted through the timing belt 23 and the timing pulleys 21, 22 to the cam shafts 19, 20 so that the cam shafts 19, 20 rotate.
Thus, the intake valve 17 and the exhaust valve 18 are driven to open and close in synchronism with the rotation of the crank shaft 5 and the vertical movements of the piston 4.
That is, the valves 17 and 18 are driven at predetermined opening and closing timings in synchronism with a series of four strokes: an intake stroke, a compression stroke, an explosion (expansion) stroke and an exhaust stroke, in the internal combustion engine 1.
A cam angle sensor 24 is installed in the vicinity of the intake side cam shaft 19, and outputs a cam angle signal SGC for detecting an operating timing (valve timing) of the intake valve 17.
A signal rotor 25 is integrally connected to the intake side cam shaft 19, and has, at its outer circumference, four teeth 25a made of a magnetic substance arranged at intervals of a 90.degree. rotational angle. The cam angle sensor 24 outputs a pulsed cam angle signal SGC whenever any of the teeth 25a passes in front of the cam angle sensor 24.
A throttle valve 26 is installed in the middle of the intake passage 15 and is operated by the accelerator pedal (not shown) to open and close, thereby adjusting the air flow rate into the internal combustion engine 1, that is, an intake air amount Q.
A throttle sensor 27 is connected to the throttle valve 26 to sense the throttle opening degree .theta..
An intake air amount sensor 28 is placed on the upstream side of the throttle valve 26 to detect the intake air amount Q flowing in the intake passage 15 according to, for example, a thermal method.
A surge tank 29 is formed on the downstream side of the throttle valve 26 to suppress the intake pulsation.
Each of injectors 30 is individually placed in the vicinity of the intake port 13 of each of the cylinders to inject fuel so that an air-fuel mixture is supplied into the interior of the combustion chamber 8. Each of the injectors 30 is composed of a solenoid valve which assumes an open condition in response to energization. The injector 30 receives the supply of fuel sent under pressure from a fuel pump (not shown).
In the operation of the internal combustion engine 1, simultaneous with the introduction of air into the intake passage 15, each of the injectors 30 injects fuel into the intake port 13.
As a result of this, an air-fuel mixture is produced in the intake port 13, and is introduced upon the opening of the intake valve 17 into the combustion chamber 8 during the intake stroke.
A variable valve timing actuator (which will be referred to hereinafter as a VVT actuator) 40 is connected to the intake side cam shaft 19, and is driven by an operating oil (lubricating oil) to change the valve timing (i.e., opening and closing) of the intake valve 17 and/or the exhaust valve 18.
The VVT actuator 40 changes the displacement angle of the intake side cam shaft 19 with respect to the intake side timing pulley 21, thereby changing the valve timing of the intake valve 17.
An oil control valve (which will be referred to hereinafter as an OCV) 80 supplies the operating oil to the VVT actuator 40, and also adjusts the amount of the operating oil supplied thereto.
An electronic control unit (which will be referred to as an ECU) 100 is composed of a microcomputer (which will be described herein later), and is designed to drive various types of actuators (the injectors 30, the igniter 11, the OCV 80 and the like) on the basis of various sensor signals (the intake air amount Q, the throttle opening degree .theta., the coolant temperature W, the crank angle signal SGT, the cam angle signal SGC and the like) representative of operating conditions of the internal combustion engine 1, thus controlling the fuel injection amount, the ignition timing, the valve timing and the like in the internal combustion engine 1.
Secondly, referring to FIGS. 12 to 17, description will be made hereinbelow of the concrete configuration of a variable valve timing mechanism including the VVT actuator 40 and the OCV 80.
FIG. 12 is a cross-sectional view showing a configuration in the vicinity of the intake side cam shaft 19 with the WT actuator 40 installed. In this illustration, a configuration of an operating oil supply mechanism (OCV 80) for driving the VVT actuator 40 is also shown.
In FIG. 12, parts identical to those mentioned above are marked with the same reference numerals. The VVT actuator 40 adjusts the intake valve timing, while the OCV 80 controls the amount of the operating oil to be supplied to the VVT actuator 40. The intake side timing pulley 21 rotates in synchronism with the crank shaft 5 through the timing belt 23 which rotates together with the crank shaft 5.
Through the VVT actuator 40, the rotation of the intake side timing pulley 21 is transmitted to the intake side cam shaft 19.
A bearing 41 is fixedly secured to the cylinder head 3 (see FIG. 11) to support the intake side cam shaft 19 rotatably.
A first oil passage 42 and a second oil passage 43 are provided in the intake side cam shaft 19 and a rotor 52 (which will be described herein later).
The first oil passage 42 communicates with a retarding chamber 62 (which will be described herein later) which is for shifting the rotor 52 in a retardation direction, while the second oil passage 43 communicates to an advancing chamber 63 (which will be described herein later) for shifting the rotor 52 in an advance direction.
An oil pump 91 pumps the operating oil (lubricating oil) from an oil pan 90 which stores the operating oil, and an oil filter 92 purifies the pumped operating oil. The oil pan 90, the oil pump 91 and the oil filter 92 constitute a lubricating means for lubricating the moving parts of the internal combustion engine 1 (see FIG. 11), and constitutes a means for supplying operating oil to the VVT actuator 40 in cooperation with the OCV 80.
Various types of sensors 99 include the aforesaid crank angle sensor 6 and the like provided in conjunction with the internal combustion engine 1, and input to the ECU 100 various sorts of operating conditions information of the internal combustion engine 1 such as the crank angle signal SGT.
A spool valve 82 slides within a housing 81 of the OCV 80. A linear solenoid 83 causes the spool valve 82 to slide in accordance with a control signal from the ECU 100. A spring 84 biases the spool valve 82 in a direction opposite the direction of the linear solenoid 83.
Ports 85 to 87, 88a and 88b are formed in the housing 81.
The supply port 85 communicates through the oil filter 92 to the oil pump 91, while an A port 86 communicates to the first oil passage 42, a B port 87 communicates with the second oil passage 43, and the discharge ports 88a, 88b are coupled to the oil pan 90.
In the operation of the internal combustion engine 1, when the oil pump 91 operates in connection with the rotation of the crank shaft 5, the operating oil in the oil pan 90 is sucked and discharged therefrom.
The operating oil discharged is sent through the oil filter 92 and selectively supplied to the oil passages 42, 43 by the OCV 80.
The oil amounts in the oil passages 42, 43 are increased/decreased in a manner such that the opening degrees of the ports 86, and 87 are varied continuously by the sliding motion of the spool valve 82. At this time, each port opening degree is determined by a current value i (controlled variable) to be applied to the linear solenoid 83.
The ECU 100 controls the current i to be given to the linear solenoid 83 on the basis of signals from various types of sensors such as the crank angle sensor 6 and the cam angle sensor 24.
A housing 44 of the VVT actuator 40 is installed to be rotatable relative to the intake side cam shaft 19, while a case 45 is fixedly secured to the housing 44.
A back spring in the form of plate spring 46 is located between a tip seal 49 (which will be described herein later) and the case 45 to press the tip seal 49 against the rotor 52 (which will be described herein later).
A cover 47 is fixed through a bolt 48 to the case 45. The bolt 48 fixes the housing 44, the case 45 and the cover 47.
The tip seal 49 is pressed against the rotor 52 by the back spring 46 to prevent movement of the operating oil between hydraulic chambers defined by the rotor 52 and the case 45. A plate 50 is fixed through a screw 51 to the cover 47.
The rotor 52 is fixed to the intake side cam shaft 19, and is located to be rotatable relative to the case 45.
A column-like holder 53 is provided in the rotor 52, and has a recess portion which engages with a plunger 54 (which will be described herein later).
The plunger 54 comprising a projecting member is caused slide within the housing 44 by the resiliency of a spring 55 (which will be described hereinbelow) and an oil pressure introduced into the holder 53.
The spring 55 biases the plunger 54 toward the rotor 52. A plunger oil passage 56 accepts the operating oil for applying an oil pressure to the plunger 54 against the biasing force of the spring 55. An air hole 57 normally sets the spring 55 side of the plunger 54 at atmospheric pressure.
A connecting bolt 58 fixedly connects the intake side cam shaft 19 and the rotor 52. Further, a shaft bolt 59 fixedly connects the intake side cam shaft 19 and the rotor 52 through rotational axes thereof. The shaft bolt 59 is placed to be rotatable with respect to the cover 47.
An air passage 60 is formed in the shaft bolt 59 and the intake side cam shaft 19 to set the inner side of the plate 50 at a pressure equal to atmospheric pressure.
FIG. 13 is a partial cross-sectional view showing a state where oil pressure is applied through the plunger oil passage 56 to the plunger 54.
As FIG. 13 shows, the plunger 54 is pressed to the housing 44 side by the oil pressure while compressing the spring 55, whereupon, the plunger 54 and the holder 53 are released from their engagement, so that the rotor 52 becomes rotatable with respect to the housing 44.
FIG. 14 is a cross-sectional illustration taken along the line X--X of FIG. 12 as viewed from the arrows, FIG. 15 is a partial cross-sectional view showing a shifted state of a slide plate, FIG. 16 is a cross-sectional illustration taken along the line Y--Y of FIG. 12 as viewed from the arrows, and FIG. 17 is a cross-sectional illustration taken along the line Z--Z of FIG. 12 as viewed from the arrows.
In FIGS. 14 to 17, the bolt 48 engages in a bolt hole 61. The retarding chamber 62 rotates first to fourth vanes 64 to 67 (which will be described herein later), integrated with the rotor 52, in the retardation direction.
The retarding chambers 62 are provided so as to be surrounded by the rotor 52, the case 45, the cover 47 and the housing 44, and the correspond to the first to fourth vanes 64 to 67 respectively. Further, the retarding chambers 62 communicate with the first oil passage 42 to receive the operating oil through the first oil passage 42.
The sector-shaped advancing chambers 63 also rotate the first to fourth vanes 64 to 67. The advancing chambers 63 are provided so as to be surrounded by the rotor 52, the case 45, the cover 47 and the housing 44, and corresponding to each of the first to fourth vanes 64 to 67 respectively. The advancing chambers 63 communicates with the second oil passage 43 to receive the operating oil through the second oil passage 43.
In accordance with the amount of operating oil supplied to the retarding chamber 62 and the advancing chamber 63, the rotor 52 shifts relative to the housing 44 so that the respective volumes of the retarding chambers 62 and advancing chambers 63 can be varied.
The first vane 64 is formed to protrude radially outward from the rotor 52. The holder 53 is fitted in the housing 44 side of the first vane 64, while a communication oil passage 70 (which will be described herein later) is recessed in the cover 47 side thereof.
In the middle of the communication oil passage 70, a shift groove 72 (which will be described herein later) is recessed. The plunger oil passage 56 passes through from the shift groove 72 through the holder 53 to the housing 44 side.
Each of the second to fourth vanes 65 to 67 is formed to protrude radially and outwardly from the rotor 52.
A tip seal 73 (which will be described herein later) is provided at the portions of each of the first to fourth vanes 64 to 67 that come into contact with the case 45.
A vane supporter 68 constitutes a central portion of the rotor 52. A shoe 69 is formed to protrude radially inward from the case 45. The shoe 69 has the bolt hole 61 which receives the bolt 48, and the tip seal 49 is provided at a portion of the shoe 69, and comes into contact with the vane supporter 68.
The communication oil passage 70 communicates to a space between the retarding chamber 62 and the advancing chamber 63 located at either side of the first vane 64. The slide plate 71 moves within the shift groove 72 (which will be described herein later) provided in the middle of the communication oil passage 70.
The communication oil passage 70 is partitioned by the slide plate 71, thereby preventing oil leakage between the retarding chamber 62 and the advancing chamber 63.
The slide plate 71 shifts toward the advancing chamber 63 side (see FIG. 14) when the oil pressure in the retarding chamber 62 is high, while moving toward the retarding chamber 62 side (see FIG. 15) when the oil pressure in the advancing chamber 63 is high.
The shift groove 72 is recessed in the middle of the communication oil passage 70, and the plunger oil passage 56 communicates with an intermediate portion of the shift groove 72.
The plunger oil passage 56 communicates with the retarding chamber 62 when the slide plate 71 shifts to the advancing chamber 63 side (see FIG. 14), while communicating with the advancing chamber 63 when the slide plate 71 moves to the retarding chamber 62 side (see FIG. 15).
The tip seal 73 is provided for each of the first to fourth vanes 64 to 67 to accomplish the sealing between each of the vanes 64 to 67 and the case 45, thereby preventing the oil leakage.
Arrows in FIGS. 14, 16 and 17 signify a direction of rotation of the entire VVT actuator 40 by the timing belt 23 and the like.
Furthermore, a description will be given hereinbelow of concrete operations of the VVT actuator 40 and the OCV 80.
First of all, when the internal combustion engine 1 is in the stopping condition, as shown in FIG. 14, the rotor 52 is at the maximum retardation position (that is, it is driven rotationally to a maximum in the retardation direction relatively with respect to the housing 44).
In the following description, the valve timing to be taken when the rotor 52 is at a position most retarded will be referred to as being at a maximum retardation position, and the phase difference (advance amount) between an intake side cam angle and a crank angle when the valve timing is at the maximum retardation position will be referred to as a maximum retardation value.
At this time, since the oil pressure supplied from the oil pump 91 to the OCV 80 is low (or the atmospheric pressure), the oil pressure is not applied to the first oil passage 42 and the second oil passage 43.
Thus, because of no supply of the oil pressure to the plunger oil passage 56, as shown in FIG. 12, the plunger 54 is pressed against the holder 53 due to the biasing force of the spring 55 so that the plunger 54 and the holder 53 are in engagement relation to each other.
Subsequently, when the internal combustion engine 1 starts, the oil pump 91 operates to cause the oil pressure to be given to the OCV 80 to rise, so that the oil pressure is applied through the A port 86 to the retarding chamber 62. In this case, owing to the oil pressure in the retarding chamber 62, the slide plate 71 shifts to the advancing chamber 63 side, which makes a communication between the retarding chamber 62 and the plunger oil passage 56.
The plunger 54 is then pushed and moved to the housing 44 side so that the plunger 54 and the rotor 52 are released from their engagement.
Nevertheless, since the oil pressure is supplied to the retarding chamber 62, the vanes 64 to 67 are brought into contact with the shoe 69 in the retardation direction and pressed thereagainst. Accordingly, even if the engagement by the plunger 54 is terminated, the housing 44 and the rotor 52 are pressed against each other by the oil pressure in the retarding chamber 62, thus reducing or eliminating vibrations or impacts.
Next, when the B port 87 is opened to advance the rotor 52, since the operating oil is supplied through the second oil passage 43 to the advancing chamber 63, the oil pressure is transmitted from the advancing chamber 63 to the communication oil passage 70 so that the slide plate 71 is pushed by the oil pressure and is shifted to the retarding chamber 62 side.
Owing to the shifting of the slide plate 71, the plunger oil passage 56 communicates with the advancing chamber 63 side of the communication oil passage 70 so that the oil pressure is transmitted from the advancing chamber 63 to the plunger oil passage 56.
As shown in FIG. 13, due to this oil pressure, the plunger 54 moves to the housing 44 side against the biasing force of the spring 55, thereby releasing the plunger 54 and the holder 53 from their engagement.
Thus, the A port 86 and the B port 87 are opened/closed to adjust the oil amount to be supplied in a state where the plunger 54 and the holder 53 are released from their engagement, so that the oil amounts in the retarding chamber 62 and the advancing chamber 63 are adjusted to advance or retard the rotation of the rotor 52 with respect to the rotation of the housing 44.
Furthermore, referring to FIG. 18, a description will be given hereinbelow of a valve timing detecting operation.
FIG. 18 is a timing chart showing a crank angle signal SGT, a cam angle signal SGCd at the maximum retardation and a cam angle signal SGCa at advance, that is, showing a phase relationship among the crank angle signal SGT and the cam angle signals SGCd and SGCa and a method for calculation processing of a real valve timing Ta.
The ECU 100 measures a period T of the crank angle signal SGT and further measures a phase difference time .DELTA.Ta from the cam angle SGCa to the crank angle signal SGT.
In addition, according to the following equation (1), the ECU 100 calculates a maximum retardation value Td on the basis of a phase difference time .DELTA.Td in the case that the valve timing is at the maximum retardation position and the crank angle signal period T, and stores the calculation result in its RAM.
Moreover, the maximum retardation value Td signifies an advance amount in the case that the intake side valve timing is at the maximum retardation position, and this value indicates an advance amount of the intake side cam angle with respect to the crank angle in the case that the valve overlap between the intake valve and the exhaust valve comes to a minimum. EQU Td=(.DELTA.Td/T).times.180[degCA] (1)
Furthermore, the ECU 100 obtains a real valve timing Ta on the basis of the phase difference time .DELTA.Ta, the crank angle signal period T and the maximum retardation value Td according to the following equation (2). EQU Ta=(.DELTA.Ta/T).times.180[degCA]-Td (2)
In this case, the detection of the maximum retardation value Td is for the purpose of correcting the variations among the products (the variations among the cam angle sensor installations and the output signals therefrom) to calculate the correct real valve timing Ta.
A current control circuit 114 is for controlling a linear solenoid current i for the OCV 80.
A CPU 102 calculates the linear solenoid current i for the OCV 80 on the basis of various input signals, and outputs, to an output port 108, a duty signal corresponding to the linear solenoid current i for the OCV 80 on the basis of a time measurement result by a timer 107.
FIG. 19 is a block diagram showing an internal configuration of an electronic control unit in a conventional valve timing control system for an internal combustion engine.
In FIG. 19, the ECU 100 includes a microcomputer 101.
The microcomputer 101 is composed of a CPU 102 for conducting various sorts of calculations and determinations, a ROM 103 for storing predetermined control programs and the like in advance, a RAM 104 for temporarily storing the calculation results of the CPU 102, and the like, an A/D converter 105 for converting an analog voltage into a digital value, a counter 106 for measuring a period of an input signal and the like, a timer 107 for measuring a drive time of an output signal and the like, an output port 108 acting as an output interface, and a common bus 109 for establishing connections among the blocks 102 to 108.
A first input circuit 110 waveform-shapes a crank angle signal SGT from the crank angle sensor 6 and a cam angle signal SGC from the cam angle sensor 24 and inputs them to the microcomputer 101 as an interruption instruction signal INT.
The CPU 102 reads the value of the counter 106 and stores it in the RAM 104 whenever an interruption takes place due to the interruption instruction signal INT.
In addition, the CPU 102 calculates a period T (see FIG. 18) of the crank angle signal SGT on the basis of a difference between the counter value when the last crank angle signal SGT was input and the present value, and further calculates an engine speed Ne on the basis of the crank angle signal period T.
Furthermore, the CPU 102 reads out, from the RAM 104, a counter value when a cam angle signal SGC is input thereto, and calculates a phase difference time .DELTA.T on the basis of the read counter value and the counter value when a crank angle signal SGT is input thereto.
A second input circuit 111 reads in a coolant temperature W from the water temperature sensor 12, a throttle opening degree .theta. from the throttle sensor 27 and an intake air amount Q from the intake air amount sensor 28 and forwards them to the A/D converter 105 after conducting processing such as removal of noise components and amplification.
The A/D converter 105 converts the coolant temperature W, the throttle opening degree .theta. and the intake air amount Q into digital data and places the digital inputs in the CPU 102.
A drive circuit 112 outputs a control signal to drive the injector 30, while a drive circuit 113 outputs a control signal to operate the igniter 11.
The CPU 102 calculates, on the basis of the various sorts of input signals, a driving time of the injector 30 and an ignition timing of the igniter 11, and drives the injector 30 and the igniter 11 through the output port 108 and the drive circuits 112, 113 on the basis of the results of the time measurement by the timer 107, thereby controlling the fuel injection amount and the ignition timing.
A current control circuit 114 controls a linear solenoid current i for the OCV 80.
The CPU 102 calculates the linear solenoid current i for the OCV 80 on the basis of the various sorts of input signals, and further outputs, to the output port 108 a duty signal corresponding to the linear solenoid current i for the OCV 80.
The current control circuit 114 carries out control on the basis of the duty signal so that the linear solenoid current i flows in the linear solenoid 83, thus controlling the valve timing.
A power circuit 115 produces a constant voltage from a battery voltage input through the key switch 117, and the microcomputer 101 is operated by the constant voltage from the power circuit 115.
In general, a valve timing control system for an internal combustion engine is designed to conduct the valve timing control while learning a maximum retardation position of the valve timing.
In the conventional internal combustion engine valve timing control system, as operating modes there are set, for example, an idle operating mode, a low-speed operation mode, an acceleration/deceleration operation mode and the like. In these operation modes, the maximum retardation position of the valve timing is learned to control the valve timing based on the learned value of the maximum retardation position.
In the idle operation mode, the intake side or exhaust side valve timing is controlled that the valve overlap becomes a minimum. For instance, the intake side valve timing is set to a most retarded condition on the basis of the learned value of the maximum retardation position. Further, the valve timing control is implemented while this maximum retardation position is always learned.
In the low-speed operation mode or in the acceleration/deceleration operation mode, for example, in the case where the engine speed is between 1000 rpm and 5000 rpm, the intake side valve timing is advanced according to the operating situation.
For instance, in cases where the motor vehicle accelerates gradually from its stopping condition so that its speed gains, as shown in FIG. 9, the intake side valve timing is advanced gradually in accordance with the rise of the engine speed from when the engine speed exceeds 1000 rpm. Further, after the valve timing is most advanced at one engine speed, the valve timing is again retarded gradually to return to the maximum retardation position when the engine speed reaches approximately 5000 rpm.
As described above, in the conventional internal combustion engine valve timing control system, the maximum retardation position of the valve timing is learned at all times in each learning mode.
For this reason, for example, if foreign matters exist in the lubricating oil and the foreign matters get in the advancing chamber or the retarding chamber, there is a possibility that the maximum retardation position is learned in error in a state where the valve timing is not actually retarded up to the maximum retardation position. In such a case, the normal valve timing control becomes difficult, which can result in the deterioration of the operating performance and the exhaust gas purification.